In order to cope with the challenge of the wideband technique and satisfy the requirements of the new services at the same time, the 3rd Generation Partnership Project (3GPP) proposes the standard work of the LTE project, namely the LTE technique, based on the Beyond 3rd Generation in mobile communication system (B3G) technique over 10 years. In the LTE, as for the air interface technique, the Orthogonal Frequency Division Multiplexing/Frequency Division Multiple Access (OFDM/FDMA) replaces the Code Division Multiple Access (CDMA) as the multiple access technique, and the Multiple-Input Multiple-Output (MIMO) technique and the adaptive technique are largely adopted to improve the system throughput and system performance.
The cell search process is a key physical process for establishing the communication link between the user terminal and the base station in the wireless cellular system, and its main object is to make the user terminal capture the time and frequency synchronization of the situated cell, and identify the identifier of this cell and basic information broadcasted in this cell at the same time. The basic steps of the cell search in the LTE system comprises: 1) users carrying out the cell search in the central frequency band of the receiving frequency band, and obtaining the timing and cell identifier information according to the synchronization channel (SCH); 2) detecting broadcast channel (BCH) information based on the timing information maintained by the SCH and the base station, thereby obtaining other configuration information of the cell; 3) users further receiving and transmitting data on the allocated frequency band according to the obtained broadcast control information. For the SCH signal, the LTE system adopts the hierarchical synchronization search mechanism, namely including the primary synchronization channel (P-SCH) and secondary synchronization channel (S-SCH). The synchronization code in the primary synchronization channel adopts 3 Zadoff-Chu (ZC) sequences in the frequency domain, and is mainly used for carrying out the identification of the inter cell group identifier or the sector number, frequency synchronization and 5 ms timing synchronization, and at the same time, the primary synchronization sequence also acts as a pilot sequence when carrying out the coherent detection on the secondary synchronization channel; and the synchronization code in the secondary synchronization channel is generated by interleaved-mapping two short binary sequences with each other, whose main function is for cell group identifier detection and frame timing synchronization.
With reference to FIG. 1, it is a schematic diagram of the structure of the primary synchronization channel and the secondary synchronization channel.
It can be seen from the figure that the Time-Division Multiplexing (TDM) scheme is applied in P-SCH and S-SCH, each 10 ms-radio frame is sent twice, for the P-SCH, sequences sent in successive twice are consistent so as to implement the 5 ms synchronization, and for the S-SCH, sequences sent in successive twice are different so as to implement the frame timing synchronization. For the FDD-LTE, P-SCH and S-SCH are respectively situated in the last and the last but one OFDM symbols of the 0th and 10th slots; and for the TDD-LTE, the P-SCH is fixedly sent in the downlink pilot time slot (DwPTS) in the specific subframe, and the S-SCH is fixedly sent on the last OFDM symbols in the 0th and 5th subframes.
The signal sequence of the secondary synchronization channel in the LTE system can be denoted as d(0), . . . , d(61), and this sequence is generated by interleaving two 31 bits-binary sequences each other. The generated sequence is further scrambled by one group of scrambler sequences, and this scrambler sequence is determined by the sector number NID(2) in the primary synchronization signal. The subframe 0 and the subframe 5 of the sequence after the cascade of two 31 bits-sequences are different, as shown in the following formula:
      d    ⁡          (              2        ⁢        n            )        =      {                                                                                                            s                    0                                          (                                              m                        0                                            )                                                        ⁡                                      (                    n                    )                                                  ⁢                                                      c                    0                                    ⁡                                      (                    n                    )                                                                                                      in                ⁢                                                                  ⁢                subframe                ⁢                                                                  ⁢                0                                                                                                                              s                    1                                          (                                              m                        1                                            )                                                        ⁡                                      (                    n                    )                                                  ⁢                                                      c                    0                                    ⁡                                      (                    n                    )                                                                                                      in                ⁢                                                                  ⁢                subframe                ⁢                                                                  ⁢                5                                                    ⁢                                  ⁢                  d          ⁡                      (                                          2                ⁢                n                            +              1                        )                              =              {                                                                                                  s                    1                                          (                                              m                        1                                            )                                                        ⁡                                      (                    n                    )                                                  ⁢                                                      c                    1                                    ⁡                                      (                    n                    )                                                  ⁢                                                      z                    1                                          (                                              m                        0                                            )                                                        ⁡                                      (                    n                    )                                                                                                      in                ⁢                                                                  ⁢                subframe                ⁢                                                                  ⁢                0                                                                                                                              s                    0                                          (                                              m                        0                                            )                                                        ⁡                                      (                    n                    )                                                  ⁢                                                      c                    1                                    ⁡                                      (                    n                    )                                                  ⁢                                                      z                    1                                          (                                              m                        1                                            )                                                        ⁡                                      (                    n                    )                                                                                                      in                ⁢                                                                  ⁢                subframe                ⁢                                                                  ⁢                5                                                        
wherein 0≦n≦30, m0 and m1 are all determined by the physical layer cell ID group NID(1), as shown in the following formula:m0=m′ mod 31m1=(m0+└m′/31┘+1)mod 31
            m      ′        =                  N        ID                  (          1          )                    +                        q          ⁡                      (                          q              +              1                        )                          /        2              ,      q    =          ⌊                                    N            ID                          (              1              )                                +                                                    q                ′                            ⁡                              (                                                      q                    ′                                    +                  1                                )                                      /            2                          30            ⌋        ,            q      ′        =          ⌊                        N          ID                      (            1            )                          /        30            ⌋      
the result of the above formulas is as shown in table one.
Table 1 the relationship of the physical cell group number NID(1) with m0 and m1
NID(1)m0m10011122233344455566677788899910101011111112121213131314141415151516161617171718181819191920202021212122222223232324242425252526262627272728282829292930300231133224333534463557366837193881039911401012411113421214431315441416451517461618471719481820491921502022512123522224532325542426552527562628572729582830590360146125623663476458656966710678116891269101370111471121572131673141774151875161976172077182178192279202380212481222582232683242784252885262986273087048815892690379148925993610947119581296913971014981115991216100131710114181021519103162010417211051822106192310720241082125109222611023271112428112252911326301140511516116271173811849119510120611121712122813123914124101512511161261217127131812814191291520130162113117221321823133192413420251352126136222713723281382429139253014006141171422814339144410145511146612147713148814149915150101615111171521218153131915414201551521156162215717231581824159192516020261612127162222816323291642430165071661816729——————
The sequences s0(m0)(n) and s1(m1)(n) are defined by the cyclic shift of the m sequence {tilde over (s)}(n), as the following formula:s0(m0)(n)={tilde over (s)}((n+m0)mod 31)s1(m1)(n)={tilde over (s)}((n+m1)mod 31)
wherein m sequence {tilde over (s)}(i)=1−2x(i), 0≦i≦30 is defined as the x(ī+5)=x(ī+2)+x(ī))mod 2, 0≦ī≦25 and its initial state is x(0)=0,x(1)=0,x(2)=0,x(3)=0,x(4)=1.
The scramble sequences c0(n) and c1(n) are determined by the inter cell group sector number detected by the P-SCH, and are composed of the two cyclic shift sequences of the m sequence {tilde over (c)}(n):
                                                                                                    ⁢                                                                    c                    0                                    ⁡                                      (                    n                    )                                                  =                                            )                        ⁢            mod            ⁢                                                  ⁢            31                    )                ⁢                                  ⁢                                  ⁢                                            c              1                        ⁡                          (              n              )                                =                                  +            3                              )        ⁢    mod    ⁢                  ⁢    31    )
wherein NID(2)ε{0,1,2} is the physical layer cell ID in the cell group number NID(1) namely the sector number.
The scramble sequence {tilde over (c)}(i)=1 −2x(i), 0≦i≦30 is defined as x(ī+5)=(x(ī+3)+x(ī))mod 2 , 0≦ī≦25, and its initial state is x(0)=0,x(1)=0,x(2)=0,x(3)=0,x(4)=1.
The scramble sequences z1(m0)(n) and z1(m1)(n) are composed of the cyclic shift sequence of the m sequence {tilde over (z)}(n), as the following formula:z1(m0)(n)={tilde over (z)}((n+(m0 mod 8))mod 31)z1(m1)(n)={tilde over (z)}((n+(m1 mod 8))mod 31)
wherein m0 and m1 are shown in the table one, which are determined by the cell group number NID(1). The scramble sequence {tilde over (z)}(i)=1−2x(i), 0≦i≦30 is defined as x(ī+5)=(x(ī+4)+x(ī+2)+x(ī+1)+x(ī))mod 2, 0≦ī≦25, and its initial state is x(0)=0, x(1)=0, x(2)=0, x(3)=0, x(4)=1.
The secondary synchronization channel detection and frame timing synchronization scheme in the prior art is to carry out the cross correlation on the detection data on the secondary synchronization channel and the local 168×2 binary local sequence in the frequency domain according to the result of the primary synchronization channel detection, and judge out the corresponding secondary synchronization sequence or the secondary synchronization signal according the correlation peak; and then further obtain the frame timing synchronization according to the corresponding positions of the detection data on the secondary synchronization channel and the local 168×2 binary local sequence. It will take one radio frame as an example, detecting two successive secondary synchronization signals needs 2×62×168×2 times of multiplying operations and 2×62×168×2 times of addition operations, and thus its operation complexity is high; besides, in the case of the low signal to noise ratio, the mismatch of the detected physical cell group numbers corresponding to the two secondary synchronization signals possibly occurs, and thus the average of the radio frames has to be carried out a plurality of times to improve its correct detection probability, and therefore the operation complexity of the detection algorithm is further increased.